Obstructive sleep apnoea (OSA) is a sleep breathing disorder where the upper airway collapses during sleep. Most patients diagnosed with OSA are treated with continuous positive airway pressure (CPAP), which acts as an air splint to hold the upper airway open. This is delivered to the patient with a flow generator and mask system while they sleep.
Although CPAP provides effective therapy, compliance rates are suboptimal. The constant pressure provided feels unnatural and many patients have difficulty breathing out against the pressure. This reduces the patient tidal volume. Current vented masks can have a high airflow causing excess noise, airflow and high power requirements. The current solutions are complex and relatively expensive, involving a special flow generator that reduces the pressure on exhalation (e.g. Bi Level Flow Generator).
Most patients on CPAP are older. While some can afford expensive therapy many of these people are on pensions or Social Security and have limited spending money for therapy. Patients that are predisposed to not accept therapy are less likely to want to spend more money to get additional features, even if they are aimed at improving compliance. Patients may not be able to afford the high level technology and may miss out on therapy altogether.
A low level technological product would be the most effective solution as it has the lowest costs involved, but has the potential to make a significant difference. There are currently no lower technology solutions for flow or pressure reduction or modification that the patient can use on their current CPAP flow generator.
There are a few inexpensive accessories available to OSA patients on CPAP. Chinstraps can be used to minimise mouth leak that causes the upper airway to dry out making the patient uncomfortable. Chinstraps are available for around thirty dollars or less. Other solutions such as nasal sprays and earplugs can also help.
If the patient has adequate and appropriate support and education, there are only two modifications to CPAP therapy that have been shown to improve compliance. These are humidification and pressure reduction. These are regarded as high-tech solutions.
There are a variety of devices that reduce the average treatment pressure delivered to the patient. Some examples include variable pressure devices, bi-level devices, expiratory pressure relief devices and ventilators. FIGS. 1A, 1B and 1C show the basic differences between how these devices can change or maintain flow with time. Although not depicted, these devices can also change or maintain pressure differently over time. The changes can occur on different time scales.
There is currently no low-level technology that has the potential to control pressure and flow on a breath-by-breath basis to improve breathing comfort on CPAP. Although other valves and devices have been investigated as potential solutions, nothing was found that solves the problems in a manner as satisfactory as the present invention.
Pressure Regulator Devices
Referring to FIG. 2, one device currently available is the SoftX™ from Invacare Corporation. The SoftX™ is provided with the Polaris EX™ CPAP device from Invacare. The SoftX™ is not a true example of a low-technology device as it bridges the gap between a high-level technology device and a low level device. It uses a combination of electronics and a mechanical solution by using a pressure transducer to sense the pressure and open a valve to divert the flow.
The SoftX™ device does not provide pressure relief, only pressure swing reductions, as shown in FIG. 3. Additionally, the SoftX™ device does not reduce the pressure spike, only the duration of the spike. There is no evidence that pressure swing reductions is enough to improve compliance significantly. In fact, there is very little information on the effect of pressure swing reductions on compliance.
Another example of a pressure regulating device is disclosed in U.S. Pat. No. 7,036,506, to the Assignee of the instant application. This patent describes a device to control the pressure or flow rate of the air supplied to a patient during CPAP with reduced noise, flow fluctuations and response time. The flow is never restricted beyond a point regardless of the position of the vane. This device is useful as previous devices choked the flow making the motor stall and slow to start again. When the patient exhales the flow is stopped and so flow to and from the blower stops, choking the motor. This means there is a delay in the response time of the CPAP machine from exhalation to inhalation. This involves a vane that directs most of the air from the inlet port to either the exhaust port or the outlet port or fraction of air to each. The vane can be angularly rotated to change the direction of the air to the various ports. Again, this valve in not true pressure relief, as it controls and regulates the flow.
Positive End-Expiratory Pressure (PEEP) Valves
Positive End-Expiratory Pressure (PEEP) valves control positive and expiratory pressure in conjunction with a medical respiration apparatus. This is so the patient has a set preset maximum positive end expiration pressure. The valve is controlled by a spring that is biased toward a closed position to prevent exhalation flow until the threshold resistance is overcome. A soft spring is used to preload a valve disk, which covers a port that is exposed to the controlled pressure. The tension of the spring is used to adjust the valve threshold pressure over a range that is useful for a clinical application of 4 to 20 cm H2O. There have been some problems with PEEP valves as the preload deformation of the spring has to be relatively large to achieve the clinical range of pressures.
PEEP valves are suitable for use with resuscitators, ventilators and CPAP systems. The expiratory connection must be airtight so that positive pressure can be achieved during the expiratory phase. PEEP valves do not influence the inspiratory O2 concentration or the inspiratory resistance of the patient. This means that the PEEP valve is suitable for spontaneous breathing and resuscitation and can remain at the patient valve at all times.
PEEP valves simply regulate the pressure in a mask. They do not relieve the pressure below the treatment pressure during expiration. The minimum pressure the valves allow in the mask is treatment pressure, as they regulate the pressure in such a way that there are instantaneous adjustments so that the pressure in the mask is stable. PEEP valves also represent a very simple, basic pressure regulation solution. The main disadvantages are that they are loud and waste treatment pressure and humidified air. They are also large and not aesthetically pleasing.
One example of a PEEP valve for use in conjunction with a medical respiration apparatus is shown in U.S. Pat. No. 4,823,828. The PEEP valve includes an adjustable spring for establishing and maintaining the threshold pressure of exhalation. It also has a flow control valve in which the disk structure uses the dynamic pressure of the exhalation flow to assist in providing control over, and fine adjustability of, the valve disk motion. This allows the continuous supply of flow during both the inhalation and exhalation phases of the breathing cycle. The PEEP valve simply regulates the pressure and flow to provide constant pressure. U.S. Pat. No. 4,823,828 refers to the PEEP valve as a “relief” valve because it relives peaks in pressure. However, the “relief” valve of U.S. Pat. No. 4,823,828 does not drop the pressure below a treatment pressure.
Demand Valves
A demand valve is used in scuba diving equipment to supply the diver with a breath of air at normal atmospheric pressure while they are deep underwater. The valve is fed from a low-pressure hose from a chamber called the first-stage. The demand valve is also known as second stage. When the diver breathes out, the air goes from the dry side of the diaphragm and is released to the outside through one-way valves. It also has a purge button that the diver can press to depress the diaphragm to make gas flow to blow water out of the mouthpiece. The basic mechanism is illustrated in FIG. 4.
The valve is dependent on the person's breathing work and so is only triggered when the person initiates a breath. Lower breathing work means a lower effort is required to breathe so it is more comfortable and natural to breathe. The system stores gas in a chamber. This chamber is connected to a mouthpiece or a full-face mask for the diver to breathe from. One side of the chamber is a flexible diaphragm.
The valve defaults to a closed position by a spring force activated by the downstream air pressure, which is labeled A in FIG. 5. This force is just enough to overcome the difference in pressure between the downstream air and the upstream balance chamber in a scuba system. The valve detects when the diver starts to inhale. This triggers the device to open a chamber to release the gas. The diver must overcome the spring force to open the valve. Breathing in lowers the pressure inside the chamber so that the diaphragm moves to release a lever, which opens the valve. The downstream air travels through a hole leading to the balance chamber and applies an upstream force slightly less than the downstream force allowing it to open. This is labelled B in FIG. 5.
The diver then finishes inhalation and starts to exhale. Upon exhalation the pressure inside the chamber increases and the diaphragm returns to its normal position and the valve closes.
Some passive semi-closed circuit re-breathers use a form of demand valve, which senses the volume of the loop and injects more gas when the volume falls below a certain level.
Scuba demand valves are designed to work at a range of pressures that occur as the diver descends to different depths. The valve of FIG. 5 is pneumatically balanced to maintain a preferred breathing resistance throughout the dive. As the ambient water pressure reduces on accent the resistance has to increase to prevent free flow.
These systems have two elements of adjustability. The demand valve allows the diver to adjust inhalation effort as the conditions change. Also, an adjustable deflector vane diverts airflow from the valve directly into the mouthpiece for added comfort. This results in a smooth assisted inhalation that is fully adjustable.
A scuba valve system such as that shown in FIG. 5 could not be applied to a CPAP system without modification. One reason is that the driving pressures are a lot higher in the scuba mechanism, so triggering does not have to be as sensitively balanced. The pressure is stored in a container in a scuba demand valve so two stages are necessary: a pressure reduction device (discussed in more detail below) and the demand valve. In a CPAP application, this is more complex as the pressure is not stored. The valve must work on both a flow generator with pressure feedback and also a straight flow generator.
Additionally, there must not be a situation where a vacuum is introduced at the patient interface. The patient must be receiving treatment pressure at all times during inspiration and should receive a baseline pressure during expiration. This complicates triggering and the device.
In a patient device, there must also not be a purge function. This means that the diaphragm cannot be placed between the airway pressure and atmospheric pressure (in the case of scuba—water pressure). The consequence of this is that the operation of the closing spring and the diaphragm cannot remain the same as in the scuba valve, and that the placement of the diaphragm must be within the mask system.
The demand valves in ventilators are designed to meet the varying principles of the emergency medical services and rescue personal. It works according to the same principles as a scuba demand valve. This system also has a pressure relief system. The manual ventilation flow rate is fixed at 40 L/m, which meets the guidelines for resuscitation outlined by the American Heart Association. A demand valve resuscitator may be designed to provide 100% oxygen to a breathing patient, with minimal respiratory effort. It is designed to operate with flow rates up to 160 L/m and on one pressure of 50 psi or 344.7 kPa on an oxygen source. The valve also provides pressure relief for over 60 cm H20. In many current ventilators, the scuba-type actual demand valve is no longer provided. In some ventilators, the scuba-type demand valve is provided for the patient as a backup in case the machine shuts down.
While demand valves have not been applied to CPAP, they have been used in ventilators. There is no demand valve applied to CPAP applications for comfort. The demand valves used in ventilation use bottled oxygen under pressure, like a scuba demand valve. The pressures that are used are much higher than a CPAP application where the maximum pressure is generally 20 cm H20, making triggering easier. Application of demand valves to CPAP devices would involve many design challenges like triggering, comfort, flow generator compatibility, vent flow rate etc.
Solenoid Valves
A solenoid valve is a type of transducer device that converts energy into linear momentum. The valve is an integrated device that contains an electromechanical component that actuates either a valve, pneumatic or hydraulic, or a switch, which is a type of relay. Solenoid valves are usually used to control gases or fluids by shutting off, releasing, dosing, distributing or mixing. The benefits of these valves include that they are fast and safe to switch, have high reliability, a long service life, good compatibility of materials, low control power and are compact. The valves work by a mechanical switch that is activated by a magnetic coil. A solenoid valve may also be used to open and close an electric circuit, open or close a valve in a fluid pipe, or cause some mechanical action to be triggered. These by themselves could not be used to regulate the pressure, but they could help activate the device. They could also assist with minimising the cracking or activation pressure of a device.
U.S. Patent Application Publication 2004/0246649 A1 discloses a flow control valve with a magnetic field sensor. The valve is a solenoid device with a magnetic field sensor. The solenoid device includes a magnetic field generator that generates a magnetic flux that extends through a magnetic flux circuit member, formed at least in part from a ferromagnetic material and defining a gap that is effectively free of any ferromagnetic material. A magnetic flux sensor is disposed to sense a portion of the magnetic flux that extends across the gap. The solenoid device is disclosed as being implemented as a fluid flow control valve, and is not applicable to pressure relief as it would not relieve pressure on its own.
Pressure Regulation Valves
Referring to FIG. 6, a pressure regulation valve regulates the pressure using a sensing orifice. It is a large device used in industry with a similar concept as a PEEP valve. A pressure regulation valve may be preferred over a PEEP valve, as it does not blow off the pressure. However, the construction of a pressure regulation valve is more complicated than a PEEP valve. Pressure regulation valves are also used in a stage one regulator of a scuba system. However, the pressure regulation valve only regulates the duration of the pressure spike, but does not reduce the size of the pressure spike as discussed above.
One example of a flow regulation vent, or valve, for regulating flow from a pressurized gas supply is disclosed in U.S. Patent Application Publication 2004/0094157 A1, by the Assignee of the instant application. The pressure regulation valve is designed to lower CO2 re-breathing in the mask, but also could be used as a one-way valve and an anti-asphyxia valve. The valve controls vent flow to give relatively high vent flow during low pressures and low vent flow during high pressures. The valve relies on flow rate to trigger it. As the patient breathes in, the flow to the mask increases and the flap on the valve blocks the vent.
The pressure regulation valve of U.S. Patent Application Publication 2004/0094157 A1 could be applied for the purpose of expiratory pressure relief to improve comfort, as when the patient breathes out the flow to the mask decreases and the flap on the valve uncovers the vent, increasing vent flow. This means the patient is breathing out mainly against the atmospheric pressure as opposed to the treatment pressure. When the patient breathes in again the flow to the mask increases and the flap directs the flow from the CPAP device allowing treatment pressure on inhalation.
The problem with this kind of valve is that it creates a loud cyclic variation. The vent noise is loud on exhalation, when lots of air rushes through it, and quiet on inhalation. Additionally it only regulates the pressure, but does not relieve the pressure below the treatment pressure.
U.S. Pat. No. 6,080,461 discloses viscoelastic memory means and flow control valve used to produce a single-use, auto-destruct injection device. It is a memory flow control valve where the disk controls the flow by being forced opened and then reverting to its original solid shape due to its viscoelastic memory. The flow control valve of U.S. Pat. No. 6,080,461 has no applicability as a pressure relief valve in a PAP device.
There are no inexpensive alternatives to the currently available, expensive, high-level technology solutions for breathing comfort compliance. Cost is a major compliance issue for therapy. There are also no low-level technology breathing comfort devices currently available that are directed to improving compliance. Devising a low cost, low-level technology product would be beneficial for many patients.